The invention relates generally to mobility management in cordless communications systems and specifically to location updating in a cellular radio access network.
Currently under development are third generation mobile communications systems, such as the Universal Mobile Communication System (UMTS) and the Future Public Land Mobile Telecommunication System (FPLMTS), which has later been renamed as IMT-2000 (International Mobile Telecommunication 2000). The UMTS is under standardization at European Telecommunication Standards Institute (ETSI), while the International Telecommunication Union (ITU) is standardizing the IMT-2000 system. These future systems are very similar in their basic features. In the following, the UMTS system will be dealt with in more detail.
Like all mobile communications systems, the UMTS provides cordless data transmission services for mobile users. The system supports roaming, in other words, UMTS users can receive and make calls anywhere, as long as they are located within the UMTS coverage area. The UMTS is anticipated to satisfy a wide variety of future service needs, such as high-speed data services (multimedia), and video services, such as video calls. Many future services that will be needed are difficult to envision today. The use of the different services is also difficult to forecast, for which reason it is not possible to optimize the UMTS to one group of services only. One conclusion from this is that the UMTS must be constructed to be versatile and to permit further development. For this reason, a modular approach of the network architecture has been adopted, making it possible to implement the UMTS effectively in different environments.
In the present perception, UMTS is built up of two or three parts that are illustrated in FIG. 1: a UMTS access network 1 (or a UMTS base station system, UMTS-BSS) and a core network 2, 3, 4 and 5. In the following, the UMTS access network will also be generally termed a radio access network. The UMTS access network 1 is mainly responsible for things related to the radio path, i.e. it offers to a core network a radio access that is needed for cordless operation. The core network 2, 3, 4 or 5 is a conventional or future telecommunications network modified to effectively utilize the UMTS access network in cordless communication. Telecommunications networks that have been contemplated as suitable core networks include second generation mobile communications systems, such as GSM (Global System for Mobile Communication), ISDN (Integrated Services Digital Network), B-ISDN (Broadband Integrated Services Digital Network), packet data networks PDN (Packet Data Network), ATM (Asynchronous Transfer Mode), and so on.
Accordingly, the UMTS access network must be capable of providing support to various core networks, also those evolving in the future. Likewise, UMTS access networks should permit connection of various radio interfaces to a core network (narrow-band, broadband, CDMA, TDMA, etc.). Several service providers SP2 to SP5 providing different services to UMTS subscribers may be connected to the core networks 2 to 5. The core networks mainly produce bearer capabilities and the service providers SP may define their own services utilizing these bearer capabilities. In theory, the core network shall be capable of supporting services defined by any SP. This contributes to the possibility of the user being connected to one core network and being simultaneously active in different services of different service providers. The UMTS access network may also be simultaneously connected to several core networks. Consequently, the access network must be capable of supporting different core networks and/or services and their subscribers simultaneously.
One of the most important demands on cordless communication is subscriber mobility management. Because a subscriber does not have a fixed access point at cordless communication, information on a subscriber""s location at each moment must be maintained with a suitable accuracy in the registers of the network. The location data may tell for instance the subscriber""s present cell, but preferably it indicates the subscriber""s present location area comprising several cells. At a cell or location area handover, the mobile station always sends the network a location updating request, which causes an updating of location data in the registers of the network. By using larger location areas, the load caused by location updatings on the radio path can be reduced. A drawback is that paging messages have to be sent the mobile station in all cells of the location area. The size of the location area generally is a compromise between location updating signalling and paging signalling.
As stated above, the UMTS access network may be connected to more than one core network CN or the UMTS subscriber may be active in several services. Each core network may have a dedicated mobility management protocol (MM) and dedicated location areas (LA). Likewise, each service may have a dedicated location management. For this reason, the UMTS access network has to send location area identities of all core networks CN on its signalling channel. Thus each subscriber terminal, being active in one or more core networks, may monitor the broadcast location area identities of the desired core network/networks and send a location updating message to the access network when moving across the boundary of some location area. If the boundary of the location area of several different core networks is crossed simultaneously, the subscriber terminal has to send many location updating messages over the air interface, one for each core network and/or service involved. This causes significant signalling load over the radio interface. This is against normal planning objectives trying to minimize the amount of MM messages and the signalling over the radio interface in general.
At the development of the UMTS access network, an open question is how a uniform MM protocol supporting different core networks CN and services can be implemented therein and how the amount of MM messages especially over the radio interface can be minimized. An idea has been presented that the very UMTS access network should comprise some kind of a subscriber register, in which location data are managed. Even such thoughts have been presented that an access network cannot operate without dedicated registers. However, registers require dedicated interfaces in the core networks CN or to an intelligent network IN. In addition, a specific mobility management protocol should be standardized in the access network. If separate registers could be left out, standardizing and planning work would be saved, and moreover, radio access network products would be simpler and cheaper.
An object of the invention is to minimize the location updating signalling to be sent over the radio interface in the systems described above.
Another object of the invention is to avoid separate subscriber registers in a radio access network.
A feature of the invention is location updating methods according to claim 1 and 16.
Another feature of the invention is cellular radio access network according to claim 10.
A radio access network is connected to one or more core networks or services, each of them having dedicated location areas and/or location management protocols. Each cell of the radio access network sends identities of those location areas to which the cell in question belongs. A subscriber terminal monitors the broadcast location area identities and sends a location updating message to the radio access network or a core network at a handover from an old cell to a new cell, if some of the location area identities broadcast by the new cell differs from the location area identities broadcast by the old cell, the old location area identities being stored in the subscriber terminal. In the invention, the subscriber terminal sends, however, only one location updating message, irrespective of how many core networks have a simultaneously changing location area or how many different services or core networks the location updating concerns, when the subscriber terminal moves from one cell to another. On the basis of the information contained in the location updating message, the radio access network or the core network supporting said services determines the mobility managments, i.e the core networks or services, and/or location areas to which the location updating applies. Subsequently, the radio access network or the core network sends an information on the new location of the subscriber or the subscriber terminal separately to each concerned core network or service. This information can preferably be sent as a (service-specific or core network-specific) location updating message in accordance with the mobility management protocol of the core network or service. By means of the invention, the amount of location updating messsages at the radio interface can be restricted to one, regardless of the real amount of location updatings to be performed in the core networks or to the service providers. In practice, this signifies a considerable saving of the radio interface capacity. This saving is achieved irrespective of whether the radio access network has dedicated subscriber registers or not. However, the location updating according to the invention makes the implementation possible also without subscriber registers. The only feature to be required of the radio access network, or a core network, is the capability of deriving from one location updating message an information on those core networks or services and/or location areas to which the location updating applies and to send the information forward to the concerned core networks or service providers. Anyway, this does necessarily not require subscriber-specific operations or registers in the radio access network, but only some kind of a modification of a location updating message of the radio access network to location updating messages of the core networks or services. At the most, that modification requires simple tables or data records having a fixed content. Dynamic subscriber-specific data and thus subscriber registers are not necessary for the invention.
In an embodiment of the invention a location updating message sent by a subscriber terminal contains at least the identity of one changed location area. Then the radio access network checks in a search table or a similar stored data structure, whether this change of one location area of a core network or service also signifies that the location area of some other core network or service has changed. In other words, the search table or the like tells the connections between the location areas of the different core networks or services. If the subscriber terminal crossed (besides the boundary of the location area of the informed core network or service) also the boundary of the location area of some other core network, the radio access network obtains the new location areas of these other core networks or services from the search table and sends the location updating data to the concerned core networks or service providers.
In an embodiment of the invention, a location updating message sent by a subscriber terminal contains, in addition to the new location area of one core network or service, also an information on the other core networks or services to which the location updating applies. This information may be a subscriber identity for each respective core network and/or service. Then the radio access network retrieves by means of said one location area the new location areas of the other core networks informed by the subscriber terminal from the search table or the like. The information of the subscriber terminal is based, in turn, on its own observation of changing location areas of said core networks. This embodiment makes it possible to avoid, also subscriber-specifically, unnecessary location updatings in core networks or services where a subscriber terminal or a subscriber is not active at the moment. This is possible, because the subscriber terminal typically contains an information on in which core networks or services it is subscribed to or active in such a way that a location updating should be performed in the core network or service. When this information is transferred in a single location updating message to the radio access network, and the location updating is carried out in the indicated core networks or services, the location updating process can be optimize subscriber-specifically without the radio access network needing dynamic subscriber data.
In an embodiment of the invention, a location updating message sends the identities of all those location areas which have changed. No search table of the above type is then absolutely necessary in the radio access network, but only the capability of sending a new location area information in correct form to the concerned core networks or service providers. However, a drawback of this approach consists in considerably long location updating messages over the radio interface, which contributes to increasing signalling load. It is even possible that the capacity defined for the location updating message in the radio access network is not sufficient for transferring all location area data at a time.
If the location areas of different core networks are defined to completely overlap irrespective of each other, the search table or the like may also contain some information on the overlap of the location areas, with an accuracy of one cell or base station, for instance. The information on the cell or base station through which the location updating message is received is normally at disposal in the radio access network, and therefore, it is not necessary to transfer it over the radio interface.
However, the operator of the radio access network has the cell structure of the radio access network completely under control, and therefore, he can usually freely determine which cells belong to which location area. Restrictions, if any, may be for instance recommendations and needs of networks for the size of location areas, or for instance the nature of the traffic in core networks (location area must be optimized for packet data or speech, for example). For this reason, the boundaries of the location areas of the different core networks or services are defined in a preferred embodiment of the invention in such a way that, on the basis of one location area of a core network changing, the possibly changed location areas of the other core networks or services can be defined unequivocally. In the most preferred approach, the location areas of different size of the core networks are defined nested in such a way that smaller location areas of one core network or service always lie within larger location areas of another core network. On the basis of the smaller (smallest) location area, for instance, it is then possible to define unequivocally the larger location areas situated at the same place. Such a structure also reduces the need for location updatings at different times, which again reduces the signalling load over the radio interface further.
In a further embodiment of the invention, the radio access network uses for the location area identities of a core network different from those used in the core network. In other words, the radio access network can have an identity format of location areas completely independent of the core network, A need for such a solution may arise for instance from that the identity format used in the radio access network does not fit the field of the location updating message of the core network, or vice versa. The radio access network performs a modification between the different identity formats and may for this purpose comprise a table containing a description of the identity of the location area of the radio access network up to the identity used by the core network, and vice versa. An opposite measure is required for sending paging messages to the subscriber terminal.
In the same way, it is possible that the location area structure (cell structure) of the radio access network somewhat differs from the location area structure of the core network. Then the radio access network may have a table or the like, on the basis of which the cell or location area structure of the radio access network is described to the location area structure of the core network, and vice versa. In some situation, such a solution may give the operator of the radio access network more liberty of optimizing the signalling of the radio access network, irrespective of the paging properties of the core network, for instance.
In an embodiment of the invention, in which a location updating should be performed in two or more services of one or more service providers, belonging to the same core network, the only one location updating message sent by a subscriber terminal can be guided to said core network. In said core network, it is then defined on the basis of the content of the location updating message to which services the location updating applies, and separate location updating messages are sent to the corresponding service providers. Said one location updating message may contain for instance a separate subscriber identity for each service, whereby the services to which the location updating applies can be defined on the basis of these identities.